Circuit for triggering one of a plurality of common cathode coupled control circuits



July 28, 1959 P. CIRCUIT FOR TRIGGERING ONE OF A PLURALITY OF COMMON HARKEMA 2,897,357

CATHODE COUPLED CONTROL CIRCUITS led June 3, 1954 I RELAY ca/vmu. c/Rcu/r 10 \A00/T/0/VAL Cd/VTROL [Cuzco/r: i912 f/ INVENTOR PIETER HARKEMA AGENT United rates Patent Ofice Patented July 28, 1959 CIRCUIT FOR TRIGGERING ONE OF A PLURAL- 'ITY OF COMMON CATHODE COUPLED CON- TROL cmcurrs Pieter Harkema, Hilversnrn, Netherlands, assignor, by

mesne assignments, to North American Philips Company, Inc, New York, N .Y., a corporation of Delaware Application June 3, 1954, Serial No. 434,215 Claims priority, application Netherlands June 4, 1953 2 Claims. (Cl. 250-27) The invention relates to a circuit arrangement for actuating one of a plurality of individual control circuits in an automatic signalling system. Such a circuit arrangement may for example be used for the actuation of a call finder, for the establishment of a connection between a register and a marker in a cross-bar exchange, in a delay-basis arrangement, in which a plurality of selectors is waiting for a selector to start when a line is set free in the desired direction, and the like. In the circuit arrangement according to the invention each individual control circuit is associated with an electronic trigger circuit, which may occupy two electrically stable positions and which comprises a discharge tube, normally cut off in the first position and conductive in the second position and, moreover, means for increasing the voltage at the control-electrode when the tube becomes conductive, the cathodes of said tubes of the various individual control circuits being connected to a point common to the individual control circuits, to which such an indication voltage may be applied through a resistor that the tubes can become conductive. The resistor has a value such that, when one of the trigger circuits occupies the second electric position in which the associated tube is conductive, the tubes of the other trigger circuit cannot become conductive. Provision is furthermore made of means which respond when the trigger circuit proceeds to the second electric position.

It should be noted that a circuit arrangement for testing the free or busy positions of outlets of selectors or call finders is known, this arrangement comprising a trigger circuit of the kind used in accordance with the invention.

The invention will now be described with reference to the accompanying drawing, which shows one embodiment thereof.

The drawing shows part of an individual control circuit I, comprising a trigger circuit having two vacuum discharge tubes 1 and 2, the anodes of which are fed from a source V via resistors 3 and 4, whilst furthermore in series with the resistor 4 is connected the winding of a relay 5. The control-electrode of tube 1 is connected to a tapping of the potentiometer 6, 7, which is connected between the anode of tube 2 and a source of negative voltage V Likewise the control-electrode of tube 2 is connected to a potentiometer 8, 9, connected between the anode of tube 1 and the voltage source -V The cathode of tube 2 is connected to earth and the cathode of tube 1 is connected, through further circuit elements if desired, to a point common to all individual control circuits 1. Normally tube 1 is cut off in all individual control circuits and tube 2 is conductive. The control-electrode of tube 1 then has a voltage of for example -30 v. If one of the individual control circuits is to be actuated, the common point 10 is connected through the contact 11 and the resistor 12 to the source V the voltage of which is for example 60 v. The control-electrodes of the tubes 1 are then positive with respect to the cathodes, so that these tubes can become conductive. The trigger circuits then occupy, all of them, an unstable position. Owing to the conductive state of a tube 1, the voltage of the control-electrode of the associated tube 2 drops and, conversely, owing to the decrease in current of the anode of tube 2 the voltage of the control-electrode of tube 1 will increase. The trigger circuits thus tend to go over to a position in which tube 2 is completely cut off and tube 1 is conductive. From experiments it has been found, however, that invariably only one of these trigger circuits at a time is capable of going over into this position. This may be accounted for as follows. Owing to the increase in current passing through tubes 1 the potential of the common point 10 increases, so that the voltage between the control-electrodes of tubes 1 and their cathodes decreases proportionally. If two tubes of one trigger circuit are conductive at a time, this trigger circuit occupies an unstable position. This could, for example, be the case if the current through resistor 12 were distributed among the tubes 1 of the various individual control circuits. This condition can thus not be maintained. An increase in current through one of the tubes 1 causes the voltage between the control-electrodes and the cathodes of tubes 1 in the other trigger circuits to decrease. Finally only one of the trigger circuits goes over into the position in which tube 1 is conductive and tube 2 is cut 01f. The voltage of the control-electrode of this tube 1 has a value such that the potential of the common point 10 is approximately equal to earth potential, so that the potential of the control-elecrodes of tubes 1 of the further trigger circuits is greatly negative with respect to that of the cathodes. Owing to the cutting-off of tube 2 in one of the trigger circuits the associated relay 5 is deenergised, so that further operations are initiated, for example, a call finder or a selector is caused to start or the individual device concerned is connected through relays to a further device. If the cathodes of the tubes 1 are connected to the common point 10 through a selector, which is to be moved into another position subsequent to the indication of the device concerned, this connection will be interrupted, so that a second trigger circuit may respond. In this case, it is therefore necessary that the contact 11 should remain closed only for a short time.

What is claimed is:

l. A circuit arrangement for actuating one of a plurality of individual control circuits, each said individual control circuit comprising an electronic trigger circuit adapted to alternately occupy two electrically stable conditions and comprising a discharge tube having a cathode and a control electrode, means for biasing said tube to cut-0E in a first one of said conditions, means for biasing said tube for conduction in the second of said conditions, means for increasing the voltage at said control grid when said tube becomes conductive, a common point connected electrically to the cathodes of said tube of all of said individual control circuits, a source of voltage, a resistor, and actuating means comprising a switch for connecting said resistor between said common point and said source of voltage thereby to apply said voltage to all of said cathodes, said voltage having a value to enable all of said tubes to become conductive, said resistor having a value with respect to said voltage Value such that upon conduction by one of said tubes the voltage then applied to the cathodes of the remaining said tubes is such as to prevent said remaining tubes from becoming conductive, whereby only one of said tubes becomes conductive in response to the actuation of said switch.

2. A circuit arrangement as claimed in claim 1, in which each of said individual control circuits includes a responding means connected to respond when the respective control circuit changes from the first to the second of said electrical conditions.

References Cited in the file of this patent UNITED STATES PATENTS 2,390,608 Miller et a1 Dec. 11, 1945 2,411,598 Smith Nov. 26, 1946 2,489,824 Shenk Nov. 29, 1949 2,768,290 Harris et a1. Oct. 23, 1956 

